Flame - retardant rayon containing mercapto-phosphonitrilate polymer



3,532,526 FLAME RETARDANT RAYON CONTAINING MERCAPTO-PHOSPHONITRILA'IE POLYMER Leonard E. A. Godfrey, Pennington, N.J., assignor to FMC Corporation, Philadelphia, Pa., a corporation of Delaware No Drawing. Continuation-impart of application Ser. No. 566,757, July 21, 1966. This application July 14, 1969, Ser. No. 841,617

Int. Cl. C08b 21/20 US. Cl. 106-165 10 Claims ABSTRACT OF THE DISCLOSURE Flame-retardant regenerated cellulose filaments and filamentary articles containing dispersed therein a flameretardant amount of a substantially water-insoluble, liquid, mercapto-phosphonitrile polymer, and a method of preparing the filamentary articles are disclosed herein.

This is a continuation-in-part application of copending patent application Ser. No. 566,757, filed July 21, 1966, now Pat. No. 3,455,713.

It is desirable for many textile purposes to provide cellulose fibers and yarns having greatly decreased flammability. The production of rayon which demonstrates acceptable flame-retardant properties for all textile requirements, using inexpensive and commercially suitable chemical flame-retardants, has not been satisfactorily accomplished to date.

The application of various organic and inorganic flameretardants to the surface of cellulose fibers and fabrics has not produced the desired result for a number of reasons. In many instances, the chemical flame-retardant is effectively removed when the fabric is washed with Water or dry cleaned with solvents. Other flame-retardant chemicals which may be applied to the fabric surface and retained after washing are generally too costly. In other cases, the chemicals used may provide some lasting reduction in flammability but destroy fiber and fabric characteristics, such as tenacity, softness, whiteness, and dyeability, which are desirable and necessary for textile applications.

In the manufacture of rayon by the viscose method, it has been proposed to add various flame-retardant chemicals to the viscose prior to spinning. This approach presents many additional problems because of the particular chemistry of the viscose process. Accordingly, the flameretardant must be stable and inert with respect to the highly alkaline viscose and also with respect to the acid regenerating bath into which the viscose is extruded. It must not be extracted during spinning and processing. Furthermore, the added material must not interfere with the spinning process, i.e., cause clogging of the spinnerets. The rayon produced from the flame-retardant containing viscose must not be degraded in any of its properties and must have a substantially reduced flammability.

It is an object of this invention to provide a flameretardant rayon fiber without appreciable degradation of any fiber properties.

It is a further object of this invention to provide a process for preparing a flame-retardant rayon fiber which retains substantially all of the properties of ordinary rayon.

These and other objects are achieved in accordance with this invention which comprises a regenerated cellulose filament having dispersed therein a substantially 3,532,526 Patented Oct. 6, 1970 Water-insoluble, liquid phosphonitrilate polymer having the following general formula:

wherein X is an oxygen or sulfur atom, R and R are the same or different alkyl, alkenyl, arylalkyl or aryl radicals wherein the alkyl and alkenyl radicals have from one to six carbon atoms, the aryl radicals have from 6 to 10 carbon atoms and at least one X in the polymer is a sulfur atom, and n is an integer of at least 3. For example R and R include methyl, ethyl, propyl, isopropyl, butyl, isobutyl, amyl, isoamyl, hexyl, allyl, crotyl, phenyl, naphthyl and cresyl radicals. Mixed esters, wherein R and R are different radicals and a portion of the X atoms are oxygen and the remainder sulfur atoms, are included herein and, depending on the combination of radicals present, may provide superior fire retardant or other desirable properties for the regenerated cellulose filaments and fibers.

In some cases where X consists predominantly of sulfur atoms and R and R are the same, i.e., methyl groups, the polymer is a crystalline solid. Where these compounds are liquified when mixed with similar compounds such as those claimed in parent application Ser. No. 566,757, now United States Patent No. 3,455,713, they may be used for this invention. However, mixed derivatives, for example, the methylmercapto-propylmercapto derivative, are preferred since they do not tend to be crystalline solids and therefore, are more readily spun with viscose into flame retardant filaments and fibers.

The phosphonitrilate polymer of this invention is a cyclic trimer, tetramer or higher cyclic polymer, or a linear polymer and is preferably employed as a mixture of these isomers based on economy and similar performance to the pure compound.

The amount of phosphonitrilate flame retardant dispersed in the regenerated cellulose filament varies from about 5 to about 30% and preferably from 10 to 25%, based on the weight of the filament.

The method of this invention comprises incorporating the above described liquid phosphonitrilate in a viscose solution and spinning the viscose in the shape of one or more filaments into a coagulating and regenerating medium. The formed filaments are aftertreated using techniques well known in the rayon field to provide continuous filaments, fibers and yarn, as well as staple fibers. These may then be used to prepare any known textile article in which the flame-retardant property is desirable.

The flame-retardant phosphonitrilate of this invention is used as a liquid of pumpable consistency which is preferably a crude reaction product, prepared, for example, as shown herein.

The mercapto derivatives of phosphonitrilic chloride may be incorporated in viscose as such or in suitable mixtures, solutions or aqueous emulsions. Preferably a controlled amount of the flame-retardant mercapto-phosphonitrilate is injected into the viscose just prior to its extrusion through the filament forming spinnerets. The viscose is then spun into an acid bath and processed in a conventional manner.

The following examples are set forth to demonstrate this invention.

EXAMPLE I The preparation of 2,2,4,4,6,6-hexaethylmercaptocyclotriphosphazatriene (hexaethylmercapto derivative of trimeric phosphonitrilic chloride) was as follows: sodium metal (20 g.) was heated in toluene (3001 ml.) until it melted, then dispersed into droplets by rapid stirring. The suspension was allowed to cool to room temperature, the toluene then decanted off, and the sodium washed with tetrahydrofuran. Tetrahydrofuran (400 ml.) was then added followed by ethylmercaptan (9-2 ml.) over a 30 minute period at room temperature. The reaction mixture was then boiled under reflux for 6 hours by which time all the sodium added dissolved.

The suspension of the sodium salt was stirred at room temperature and a solution of trimeric phosphonitrilic chloride (150 g.) in tetrahydrofuran was added. There was little or no rise in temperature. The reaction mixture was then boiled under reflux for 7.5 hours. A sample of the material was taken, worked up, set for analysis, and found to contain 0.49% residual chlorine.

The main reaction mixture was then refluxed an additional 6 hours before tetrahydrofuran was stripped off under vacuum on a rotary evaporator. The residue was poured into ice water (500 ml.) and the product extracted twice with ether (2-250 ml.). The ether solutions were washed several times with water, combined, dried under sodium sulfate and Drierite, filtered and evaporated.

under vacuum. The residue was then held under vacuum for 1 hour (40 C.0.02 mm.). A slightly off-waterwhite, fairly mobile oil was obtained (108 g.).

Elementary analysis of the product found: carbon, 28.7%; hydrogen, 6.17%; chlorine, 0.59%; nitrogen, 8.3%; phosphorus, 18.8%; and sulfur, 36.4%. It was calculated that the product would have the following percentage of elements: carbon, 28.7%; hydrogen, 6.03%; chlorine, 0.0%; nitrogen, 8.3%; phosphorus, 18.5%; and sulfur, 38.4%.

A compound prepared in the above manner was injected into the viscose line supplying the spinnerets for manufacturing rayon, in a metered amount based on the weight of the cellulose in the viscose. This viscose was spun into a conventional aqueous acid spin bath comprising 9% sulfuric acid, 2% zinc sulfate and 15% sodium sulfate at 55 C. The resulting yarn was processed by passing it through a series of baths including water wash, desulfurization bleaching, bleach acid, anti-chlorine, and soft finish baths. The 300 filament-200 denier yarn was dried and collected.

A yarn flammability test was conducted with yarn produced as described above. The test consisted of first preparing a yarn bundle by wrapping the yarn around the closed fingers of an extended hand to produce a bundle of 6000 denier and then removing it from the hand. The yarn bundle is twisted five times and then doubled on itself to produce an integrated yarn bundle, one and onehalf inches long and of 12,000 denier size. The free ends of the yarn bundle are clamped in forceps, and the bundle, held in horizontal position, is passed through the tip of the flame of a Fisher burner in an oscillating motion at a rate of one pass per second. The burner flame is adjusted to a two inch height and a blue flame. The number of passes to induce flaming of the sample is determined. A control yarn bundle (yarn contains no flame-retardant) inflames in 1 or 2 passes and flame-retardant yarns are classified for inflammability as follows:

1-2 passes-poor 3-4 passes-fair 5-6 passes-good 79 passesvery good to excellent 10 or more passesexcellent Rayon yarn containing about of the 2,2,4,4,6,6- hexaethylmercaptotriphosphazatriene was rated good in the above test with no evidence of after-glow. After-glow represents combustion without a visible flame.

Retention of the amount of flame-retardant in the yarn after the above described complete processing of the spun yarn based on phosphorus analysis showed 80.8%. The yarns esthetic properties were substantially the same as ordinary rayon.

4 EXAMPLE u The preparation of the ethylmercapto ester of mixed polymeric phosphonitrilic chlorides was as follows:

Sodium metal (276 g.) was converted into small discrete globules by cooling a molten dispersion in hot toluene. The toluene was then decanted away and the sodium particles washed with tetrahydrofuran. Tetrahydrofuran (5500 ml.) was then added followed by dropwise addition of ethylmercaptan (1115 g.). The temperature of the mixture rose gradually to and was held there to the end of the addition period. When the addition was complete, the reaction mixture was heated at 60 under reflux cooling until all the sodium had dissolved.

A mixture of linear and cyclic phosphonitrilic chlorides (464 g.), previously prepared by the action of phosphorus pentachloride on ammonium chloride in a high boiling chlorinated solvent, was dissolved in tetrahydrofuran (500 ml.) and the resultant solution added dropwise with stirring. There was suflicient heat of reaction to bring the temperature to between 60 and where it was held for the duration of the addition. Afer the addition was complete, the reaction mixture was stirred and heated under reflux for a total of 40 hours. Samples of the reaction mixture were removed from time to time and worked up to check the rate at which the chlorine content of the organic material was diminishing.

When the reaction appeared to be complete, most of the solvent was removed under vacuum, the residue poured onto ice and water, and the mixture, then acidified with dilute hydrochloric acid. The oil layer which separated was removed and the aqueous layer extracted twice with toluene. The toluene extracts were then combined with the oil that had been previously separated and the whole washed with water. After drying with anhydrous sodium sulfate, most of the toluene was distilled away under vacuum and the residual oil filtered through a little diatomaceous earth. The remainder of the volatile matter present was then removed by holding the residue under a vacuum of 0.02 mm. for one hour at 40 C.

Elementary analysis of the product found carbon, 30.1%; hydrogen, 6.5%; chlorine, 1.2%; phosphorus, 18.0%; nitrogen, 6.7%; sulfur, 35.3%. It was calculated that the product should have the same percentage of elements as the material prepared from the trimeric phosphonitrilic chloride: carbon, 28.7%; hydrogen, 6.03%; chlorine, 0.0%; nitrogen, 8.3%; phosphorus, 18.5% and sulfur, 38.4%.

The product prepared as set forth above was pumped into the viscose prior to spinning and the spun yard was completely processed as set forth in Example I. At a loading of about 15% flame-retardant the yarn was shown to have good flame retardency with no after-glow. At about 20% loading the yarn had very good flame retardency in the test with no after-glow. The yarn properties were substantially as good as ordinary rayon.

Some of the mercapto esters described herein will be more permanently retained in the yarn after continued washing of dry-cleaning operations than others and some will require addition in greater amounts to the viscous to obtain the desired flame retardency but the greatest advantage of this flame retardant material is that it can be injected into viscose and spun into a yarn which retains its normal softness and hand. Those mercapto esters of this invention which are not permanently retained by fabrics made of the rayon yarn containing the esters will be useful for incorporation in rayon intended for use in fabrics employed for disposable garments and the like.

I claim:

1. Regenerated cellulose filaments and filamentary articles, said filaments having dispersed therein a flame retardant amount of a substantially water-insoluble, liquid phosphonitrilate polymer having the following general formula:

L ri lat L wherein X is an oxygen or sulfur atom, R and R are the same or different alkyl, alkenyl, arylalkyl or aryl radicals wherein the alkyl and alkenyl radicals have from 1 to 6 carbon atoms, the aryl radicals have from 6 to 10 carbon atoms, and at least one X atom in the polymer is sulfur; and n is an integer of at least 3.

2. The regenerated cellulose filaments of claim 1 containing from about to about 30% based on the weight of the cellulose, of the liquid phosphonitrilate polymer.

3. The regenerated cellulose filaments of claim 1 wherein all of the X-atoms in the polymer are sulfur.

4. The regenerated cellulose filaments of claim 1 wherein R and R are ethyl radicals.

5. The regenerated cellulose filaments of claim 1 wherein R and R are different radicals.

6. A method of preparing a flame-retardant regenerated cellulose filament which comprises mixing viscose and a flame retardant amount of a substantially water-insoluble, liquid phosphonitrilate polymer having the following general formula:

wherein X is an oxygen or sulfur atom, R and R are the same or different alkyl, alkenyl, arylalkyl or aryl radicals wherein the alkyl and alkenyl radicals have from 1 to 6 carbon atoms, the aryl radicals have from 6 to 10 carbon atoms and at least one X atom in the polymer is sulfur and n is an integer of at least 3; shaping the mixture into a filament, and coagulating and regenerating said filament.

7. The method of claim 6 wherein the viscose is passed under pressure to a spinneret and extruded, and the liquid phosphonitrilate polymer is injected at a controlled rate into the viscose prior to extrusion.

8. The method of claim 6 wherein about 5 to about 30% of the liquid phosphonitrilate is mixed with the viscose, based on the weight of the cellulose in the viscose.

9. The method of claim 6 wherein R and R are ethyl radicals.

10. The method of claim 6 wherein the X atoms are all sulfur.

References Cited UNITED STATES PATENTS 8/1966 Schappel et al. 7/1969 Godfrey.

JULIUS FROME, Primary Examiner L. B. HAYES, Assistant Examiner UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3, 532, 526 Dated October 6, 1910 Inventor(s) Leonard E. A. Godfrey It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In the "ABSTRACT OF THE DISCLOSURE", Column 1, line 19, "phosphonitr'ile" should be -phosphonitrilate--; Column 4, line 51, hange "yard" to --yar-n--.

CHINE!) W9 SEALED Mil-W Z 1m of he Attosfina Officer FORM po'wso USCOMM-DC 60376-969 \LS. GOVIRNHINT PRl'l'llG OFFICE 1" O-QGi-JJI 

